Integrated circuits (I/Cs) include contacts to provide electrical connectivity to operate the integrated circuit devices. The contacts are typically made of metal that has good conductivity, such as copper, aluminum, or gold. Copper and aluminum are used frequently in circuits based on silicon, whereas gold is commonly used in circuits based on compound semiconductors (III-V materials.) Gold provides low contact resistance for III-V materials. Copper and aluminum do not generally form low-resistance contacts with III-V materials as well as gold.
However, gold is a contaminant in any fab or facility that uses CMOS (complementary Metal-oxide-semiconductor) processing. CMOS processing typically uses silicon, and gold diffuses very well into silicon, even from underneath a wafer being processed. The diffusion of gold into the silicon allows electrons to get into the semiconductor band gap, which contaminates the resulting transistor or other I/C device structures, causing circuit failure. Thus, gold cannot be used in any equipment used in the large-scale CMOS processing (such as a fab).
Other materials that can be used to make contacts in processes compatible with CMOS processing equipment do not have the low contact resistance of gold. Thus, the material with the desired contact properties and low contact resistance (gold) is not compatible with large-scale, mass production processing techniques that would be used to make I/Cs needing such contacts.
Descriptions of certain details and implementations follow, including a description of the figures, which may depict some or all of the embodiments described below, as well as discussing other potential embodiments or implementations of the inventive concepts presented herein. An overview of embodiments of the invention is provided below, followed by a more detailed description with reference to the drawings.